The present invention relates to injection molding machines, and in particular, to a system that transports molten plastic to molding chambers of stack molds in an off-center location, or when the transfer of the molten plastic needs to be in the center of the mold as in a split sprue bar.
For injection molds having two or more cavities, it is desired to ensure that molten plastic reaches all molding chambers at the approximately same time, or at least such that preferential flow to any one of the molding chambers is minimized. For most injection molds, molten plastic is transferred from the stationary machine platen to the stationary side of the injection mold and to the molding chamber(s). For stack molds as the one shown in FIG. 1 (prior art), molten plastic is transferred through the sprue, into a long sprue bar extending to the manifold, located in the center of the mold, which then transfers it equally to all cavities involved.
However, for stack molds as the ones shown in FIG. 2 (prior art) and FIG. 3 (prior art), where the centerline of molding chambers coincides with centerline of mold, molten plastic cannot reach the manifold directly along the centerline, but rather must take a detour route and enter the manifold at an offset location. For such stack molds, a system is needed to ensure a proper flow of molten plastic to the molding chambers.